The River Why by David James Duncan is ultimately a coming-to-life story about a child fishing prodigy and his search for happiness and fulfillment.

A child of two proficient fishing parents, Augustine "Gus" Orviston is a fishing prodigy, catching his first large fish at the age of four and his first steelhead on a fly at the age of six. His mother, Ma, fishes only in the bait-and-hook style, while his father H20, fishes in the fly-fishing style. For this reason, Gus is proficient in both styles. However, instead of embracing the differences of their fishing styles, Gus is tormented by his parents' constant bickering and arguments over which style is best, including a constant interpretation of The Compleat Angler by Izaak Walton, a pivotal book in fishing and to the Orviston family.

Gus leaves his family after school to get his own house by the Tamanawis River to execute the Ideal Schedule in fishing. He comes up with a specific plan with all the hours of his day to maximize his fishing time while simultaneously keeping an exact fishing notebook on the number of fish he has caught.

After Gus comes across a dead fisherman named Abe, he starts to question his relationship to fishing and with Life in general. From there, he resolves to be less solitary, introducing himself to all of his neighbors and finding out answers to bigger questions like whether or not there is a higher being.

Along the way, Gus also falls in love with a woman named Eddy who helps to show him the true meaning of love and the presence of a higher being in his life.